How to activate multiboot when using “Vim_Ubuntu-server-16.04_Linux-Mainline-4.12-rc6_V170624_Pre-alpha” u-boot?
I have had Android u-boot but was using LibreELEC from @kszaq and with Android u-boot I was able to activate multiboot. Now with Ubuntu server alpha on eMMC and its u-boot I am not sure.

I have serial access to khadas vim pro so u-boot commands are not problem to enter.

Also can someone actually explain what activating multiboot actually do to u-boot? Does it only set env`s or install something to?

Goal: is to run Ubuntu Server from eMMC when no microSD (LibreELEC) is pluged in. Please note this microSD have LibreELEC configured I would not like to lose any data on this microSD.

This is how printenv on Khadas VIM Ubuntu server image looks like:
Vim_Ubuntu-server-16.04_Linux-Mainline-4.12-rc6_V170624_Pre-alpha